WebAssembly _start or crt_constructor not get called.

[kinke]

I don't know about _start(), but please don't expect 
`pragma(crt_constructor)` to work. As the name says, these 'C 
runtime constructors' are normally invoked by the C runtime entry 
point, before calling the C main, all of which doesn't apply to 
WebAssembly or any other bare metal target.